Low temperature-low pressure naphtha reforming process

ABSTRACT

A hydrocarbon feedstock comprising naphthenes is catalytically reformed using a catalyst which promotes both dehydrogenation and isomerization. Cracking and other undesirable side reactions are substantially avoided by employing a reaction temperature in the range of 600* to 700*F and a hydrogen pressure not exceeding about 4 atmospheres. If the hydrogen partial pressure is about 1 atmosphere or less, satisfactory conversion of the naphthenes to aromatics is obtained without further steps. If the hydrogen partial pressure is between about 1 and about 4 atmospheres, the aromatics are adsorbed on a zeolite or other suitable substance as they are formed, thus shifting the equilibrium and promoting the dehydrogenation and isomerization reactions. The adsorbed aromatics are subsequently desorbed by, for example, heated hydrocarbon vapor. If the adsorption/desorption is used, a dual reactor set-up may be conveniently employed.

[ LOW TEMPERATURE-LOW PRESSURE NAPHTHA REFORMING PROCESS Albert B.Welty, Jr., Westfield, NJ.

[73] Assignee: Exxon Research and Engineering Company, Linden, NJ.

Mar. 7, 1973 [75] Inventor:

[22] Filed:

[21] Appl. No.: 338,992

[52] US. Cl 208/139, 208/137, 208/138, 208/141, 208/310, 260/674 SA [51]Int. Cl Clog 35/06, ClOg 25/00 [58] Field of Search 208/137, 138, 139,141, 208/310; 260/674 SA [56] References Cited UNITED STATES PATENTS2,816,939 12/1957 Nozaki 208/138 2,870,083 1/1959 Elliot 208/1382,967,823 l/l961 Langenbeck et a1. 208/137 2,972,643 2/1961 Kimberlin eta1. l 260/6735 3,125,503 3/1964 Kerr et al 208/15 3,364,137 1/1968Bercendorf et al...... 208/139 3,372,108 3/1968 Epperly et a1. 208/1413,562,147 2/1971 Pollitzer et al.... 208/139 3,574,091 4/1971 Hayes208/138 [451 Dec. 10, 1974 Primary Examiner-Delbert E. Gantz AssistantExaminer-James W. Hellwege Attorney, Agent, or FirmL. A. Proctor [57]ABSTRACT A hydrocarbon feedstock comprising naphthenes is catalyticallyreformed using a catalyst which promotes both dehydrogenation andisomerization. Cracking and other undesirable side reactions aresubstantially avoided by employing a reaction temperature in the rangeof 600 to 700F and a hydrogen pressure not exceeding about 4atmospheres. If the hydrogen partial pressure is about 1 atmosphere orless, satisfactory conversion of the naphthenes to aromatics is obtainedwithout further steps. If the hydrogen partial pressure is between about1 and about 4 atmospheres, the aromatics are adsorbed on a zeolite orother suitable substance as they are formed, thus shifting theequilibrium and promoting the dehydrogenation and isomerizationreactions. The adsorbed aromatics are subsequently desorbed by, forexample, heated hydrocarbon vapor. If the adsorption/desorption is used,a dual reactor set-up may be conveniently employed.

21 Claims, 3 Drawing Figures LOW TEMPERATURE-LOW PRESSURE NAPHTHAREFORMING PROCESS This invention relates to the catalytic conversion ofhydrocarbon fractions boiling in the motor fuel range to obtain productsof higher octane value. More specifically, this invention relates to animproved process for the catalytic reforming of naphthenes andparticularly to a process which avoids undesirable side reactions suchas cracking.

Hydroforming is a well known and widely used process for treatinghydrocarbon fractions boiling within the motor fuel or naphtha range toupgrade them, primarily by increasing their aromaticity, thus improvingtheir anti-knock characteristics. By hydroforming is ordinarily meant anoperation conducted at elevated temperatures and pressures in thepresence of solid catalyst particles and hydrogen, whereby thehydrocarbon fraction is increased in aromaticity. This increase inaromaticity arises from the conversion of the cyclohexanes andcyclopentanes, i.e., the naphthenes, as well as of paraffins, toaromatics. Aromatics concentrationalso occurs as a consequence ofcracking nonaromatics to gas. The aromatics concentration requiredvaries depending on feedstock, but typically 57 Vol.% aromatics willgive about 90 clear Research Octane Number and 70 vol.% about 100. Ifthe feed contains sufficient aromatics plus naphthenes, high octanenumber can be obtained without paraffin conversion. Hydroformingoperations are ordinarily carried out in the presence of hydrogen-richrecycle gas and in the presence ofa suitable reforming catalyst attemperatures ranging from about 750to 1,050F with pressures of formatleast about 50 pounds per square inch to sometimes as high as 800 poundsper square inch.

A major problem encountered in catalytic hydroforming is the occurrenceof cracking, which results in a reduction in the yield of liquidproduct. Hydrocarbon gaseous products, i.e., methane, ethane, propaneand butane which are less valuable than liquid product, result from thiscracking side reaction. lmportantly too, hydrogen is consumed whencracking occurs, thus reducing the yield of this valuable product.Therefore, it is desirable to minimize the cracking reaction,particularly where the feedstock to the hydroforming reactionv isespecially valuable as in the case of hydrocrackate.

The desirable reactions which occur in the reforming process, listed inorder to decreasing reaction rates are as follows:

(1) dehydrogenation of cyclohexanes to aromatics; (2) isomerization ofcyclopentanes to cyclohexanes; (3) isomerization of straight chainparaffins to branched paraffins; and (4) dehydrocyclization of paraffinsto aromatics. This invention is concerned primarily with reactions (1)and (2). Secondarily, the invention is also concerned with reaction (3).Maximum yield of high octane product will be obtained when these desiredreactions are maximized and undesirable cracking is minimized oreliminated.

Accordingly, it is a principal object of the present invention toprovide an improved catalytic reforming process which will increase thearomaticity of a hydrocarbon fraction boiling within the motor fuelboiling range but which will not result in any substantial amount ofcracking. Other objects of this invention will be apparent from aconsideration of the following descriptive material.

U.S. Pat. No. 3,577,474 to Robert L. Jacobson, dated May 4, 1971discloses the use of a rhenium-platinumalumina catalyst for theproduction of benzene and toluene from C C, cycloalkanes at 50 to 750psig. pressure and a temperature of 700 to 1,050F. From the example itcan be seen that, although the addition of rhenium to theplatinum-alumina catalyst represents an improvement, substantialcracking still occurs. In U.S. Pat. No. 3,669,875 dated June 13, 1972,Charles J. Plank, Pharez G. Waldo and Harry G. Doherty disclose a twostage reforming operation in which the first stage is primarily foreffective naphthene dehydrogenation. pressure is to 600 psig. andtemperature 800 to 1,050F. At these conditions cracking still occurs.Reference is made also to Catalyst, Volume Vl, Edited by Paul H. Emmett,published by Rheinhold Publishing Corporation, 1958 (Library of CongressCatalog No. 54-6801), pp 567-576, which shows the isomerization ofnaphthenes at 24.8 atmospheres total pressure over a temperature rangeof 547 to 734F. inthe presence of hydrogen.

It has been discovered that the desirable reforming reactions, i.e.,isomerization of cyclopentanes of cyclohexanes, and dehydrogenation ofcyclohexanes to aromatics, can be accomplished with a minimum amount ofcracking by employing reaction temperatures of about 600 to 700F. and ahydrogen partial pressure no greater than about 4 atmospheres. Thecatalyst employed is a dual function catalyst, i.e., one that promotesboth dehydrogenation and isomerization. This invention is useful inupgrading feedstocks such as petroleum naphthas, gasoline fractions,hydrocrackates, recycled reformates, and other refinery blendscontaining naphthenes, to produce high octane motor fuels.

The reforming catalysts useful for this process comprise a porousinorganic support containing catalytic amounts of platinum or othernoble metals such as rhodium, palladium or iridium, or combinations ofthese; they may be promoted by rhenium. Nickel may also be used. Whenthe catalyst is nickel, an acidicsupport is preferred, such assilica-alumina. Generally, the pre-' ferred supports are alumina andsilica/alumina. However, other supports, such as kieselguhr, magnesiumoxide, and titanium oxide may be employed. When noble metals are used,the metal components on the catalyst constitute from about 0.025 to 2.0wt.% preferably from 0.1 to 1.0 wt.%, metal on the various supports.When nickel is used, from about 1.0 to 10%, preferably about 5% is used.These catalysts maybe promoted by 0.1 1.5 wt% fluorine or chlorine.Although a platinum-chlorine-alumina is a preferred catalyst,nickel-silica-alumina or similar types may also be used. These catalystspromote both the dehydrogenation and isomerization function.

In order to promote the dehydrogenation and isomerization reactionswithout substantial cracking, the catalytic reforming process must becarried out at a temperature in the range from about 600 to about 700F.,temperatures at which the amount of cracking occurring is negligible orsmall. However, because of thermodynamic limitations, in order forsubstantial dehydrogenation to occur at this low temperature it isnecessary that the hydrogen partial pressure be maintained at a lowlevel, i.e., a level sufficiently high only to maintain adequatecatalyst activity. Hydrogen partial pressure is the total absolutepressure multiplied by the mole fraction of hydrogen in the gas phase inthe reactor. The difficulty in maintaining adequate activity will varyfrom one catalyst to another and particularly from one feedstock toanother. It is much more difficult to maintain catalyst activity withhigh boiling feedstocks than with low boiling ones. In order to obtainthe desired de gree of conversion of naphthenes, the hydrogen partialpressure should be no higher than about 4 atmospheres. If the cyclelength obtained when the hydrogen partial pressure is maintained at alevel of about 1 atmosphere or less is satisfactory with the feedstockemployed, then the isomerization and dehydrogenation reactions can takeplace to a satisfactory extent. On the other hand, if the hydrogenpartial pressure must be maintained at a level between about I and 4atmospheres in order to obtain satisfactory cycle length, then thereaction is preferably promoted by the use of an adsorbent such as azeolite to remove the aromatics as they are formed, thus shifting theequilibrium and promoting the dehydrogenation and isomerizationreactions.

Therefore, in a first aspect, this invention comprises the reforming ofa hydrocarbon feedstock comprising naphthenes at a temperature fromabout 600 to about 700F and a hydrogen pressure of about 1 atmosphere orless. A high degree of conversion of the naphthenes to aromatics isobtained, without formation of substantial amounts of cracked products.The following table shows the conversion which can be obtained atequilibrium for cyclopentane homologs.

Equilibrium Conversion of Cyclopentanes to Aromatics at 620F HydrogenPressure Atmospheres 0.1 l 3 Six-carbon cyclopentane 99.95 69 7.4

Seven-carbon cyclopentane 99.99 94 38 Eight-carbon cyclo- 99.99 991 79pcntane While not shown intthis table, the equilibrium conversion for 9+carbon cyclopentanes is more favorable than that for 8 carboncyclopentanes. Thus, at a temperature of 620F. and a hydrogen pressureof one atmosphere, an extremely high aromatic conversion can be effectedfor those compounds having 7,8 or more carbon atoms. Conversion of thesix-carbon cyclopentane, i.e. methyl-cyclopentane, would be limited to69%. However, most practical feedstocks do not contain as much methylcyclopentane as the higher molecular weight cyclopentanes; hence theconversion to aromatics over-all can be quite high. In general, thelower pressures should be used for lower molecular weight feeds, whilehigher pressures can be used for higher molecular weight feeds. it isapparent, of course, that if one can maintain the hydrogen partialpressure substantially below 1 atmosphere, one can obtain an evengreater conversion. Conversely, raising the hydrogen partial pressure to3 atmospheres does not give satisfactory results in the practice of thisaspect of the invention at this temperature levei.

This first aspect of the invention is illustrated by the followingexample, which is included here by way of illustration only and notintended as a limitation.

EXAMPLE I A comparison of the results obtained at conventional catalyticreforming conditions and at the conditions practiced in this inventionis given in this example. The hydrocrackate feed had the followingcomposition:

Billings Hydrocrackate Composition Cyclopentanes Containing 6 carbonatoms Containing 7 carbon atoms Containing 8+ carbon atoms CyclohexariesContaining 6 carbon atoms l.2 Containing 7 carbon atoms on Containing 8+carbon atoms 12.6

Benzene Toluene l Aromatics containing 8+ carbon atoms 2 Paraffins 20.5l Average carbon number 8.45 (2) Average carbon number 8.73 (3) Averagecarbon number 8.64

In reforming the Billings hydrocrackate to obtain a product having aclear Research Octane Number of 97, a conventional reforming processperformed at 930F and 400 psig. using a catalyst consisting of platinumsupported on alumina promoted by chloride gives a 90.5 vol.% yield of Cliquid product. Using the process of this invention performed at 630F,1.0 atmosphere hydrogen partial pressure, 0.25 V/V/hr using a 5.0 wt%nickel on silica-alumina catalyst having a surface area of 550 squaremeters per gram one obtains the C liquid product in a yield of 97.0%.This 6.5 vol. yield advantage means that less naphtha needs to be usedto make a given amount of gasoline, which in turn means that less crudeneeds to be used. With a high quality reforming feedstock, such asBillings hydrocrackate, the feedstock need not be subjected to anyadditional reforming operations since the 97 clear Research octanenumber is sufficient for blending into modern motor gasolines. Ofcourse, where the feedstock contains a greater amount of paraffins, anappro priate subsequent paraffin conversion step such as conventionalreforming or dehydrocyclization is also generally conducted.

A second aspect of the instant invention employs somewhat higherhydrogen partial pressures. i.e., up to about 4 atmospheres. As in thefirst aspect of this invention, the catalyst used is one which has bothdehydrogenation and isomerization functions and may be of the typepreviously described. in the second aspect, however, there is mixed withthe catalyst a solid absorbent which adsorbs the aromatic hydrocarbonsas they are formed. This shifts the equilibrium, thus promoting theformation of additional aromatics and thereby making it possible toachieve high conversion to aromatics in spite of the higher hydrogenpartial pressures employed.

Conveniently, the practice of this invention involves a dual reactorsystem. After the reforming operation in the first reactor, the feed isswitched to an identical second reactor while the aromatics are desorbedfrom the first reactor. Following desorption, the temperature of thereactor catalyst-adsorbent mixture is adjusted to that desired for thereaction and then the feed is switched back to the first reactor whilethe aromatics formed in the second reactor are desorbed. Depending uponthe time sequence employed, it may also be advantageous to employ 3 or 4reactors. It is also possible, of course, to employ a single reactorsystem. If this is done, it is necessary to interrupt the flow offeedstock whie the aromatics are being desorbed and the temperature ofthe catalyst-adsorbent mixture is adjusted.

Any solid adsorbent which has good capacity for and selectively absorbsaromatic hydrocarbons in preference to naphthenes and paraffins can beemployed in the practice of this invention. Silica gel, activated alumina and similar adsorbents can be used. However, it is preferred toemploy as the adsorbent certain natural or synthetic zeolites oraluminosilicates. Those synthetic zeolites referred to as 13x molecularsieves and available from the Linde Division of Union CarbideCorporation which contain sodium as the cation or in which certain othercations have been partially or completely substituted for the sodium,are particularly suitable. These adsorbents are made up of porous matteror crystals in which the pores are of molecular dimension and are ofuniform size. The zeolites used in the practice of this invention may bedescribed as crystalline zeolites having a rigid three-dimensionalanionic network and having interstitial dimensions of sufficient size toadsorb the aromatic compounds produced in the course of the reaction.These zeolites vary somewhat in composition but generally contain theelements silicon, aluminum and oxygen as well as an alkaline metal and-/or an alkaline earth metal element for example, sodium and/or calcium.Linde 13x molecular sieve, in which the cation is sodium and which has aB.E.T. surface area of about 760 square meters per gram and a porevolume of 0.32 cubic centimeters per gram, is suitable for this process.Even better adsorbents can be made by exchanging certain cations,particularly calcium, strontium or cadmium for all or most of thesodium. The means for preparing such cation exchanged zeolites is wellknown in the art; see, e.g., P.E. Eberly, Jr., Journal of PhysicalChemistry, Volume 66, pp 812-816 (May, 1962).

This second aspect of the invention is illustrated by FIG. 1 of theaccompanying drawing which shows schematically the reaction, desorptionand reheating steps. The naphtha feed to the reactor in the reactionstep comprises naphthenes as well as paraffins. Some hydrogen orhydrogen-containing gas is usually also fed to the reactor. In thereactor, there is present the dual function (dehydrogenation andisomerization) catalyst above described mixed with a solid such as azeolite to selectively adsorb aromatics present in the feed and theother aromatics as they are formed. The cyclohexanes are regularlyconverted to aromatics by simply dehydrogenation; the cyclopentanes areconverted first, by a ring isomerization, to cyclohexanes, and thence toaromatics. The aromatics remain in the reactor, adsorbed on thecatalyst-adsorbent mixture. Coming out of the reactor are hydrogen gasand a major portion of the paraffins. The aromatics in the feed areadsorbed preferentially at the inlet end of the bed. In addition, thearomatics made from the naphthenes are made at a greater rate at theinlet end so these aromatics are also preferentially adsorbed at theinlet end of the bed. As the adsorbent becomes saturated with aromaticsas the reaction period progresses, the adsorption front progresses frominlet to outlet of the bed. At first, during the reaction period aportion of the paraffins are adsorbed on the freshly regeneratedcatalyst-adsorbent mixture beyond the zone near the inlet where thearomatics are being adsorbed. Then, as more aromatics are adsorbed theydesorb the paraffins in a progressive wave front passing'through thebed. The isoparaffins are more easily displaced and, as a consequence,the paraffins which are most branched in structure will tend to appearfirst in the effluent and the normal paraffins will tend to appear last.Thus, by the use of proper time valves, some separation of isoparaffinsfrom n-paraffins can be achieved. This is useful because theisoparaffins have a higher octane number and may be used directly inmotor gasoline if desired, more or less selectively leaving the loweroctane number nparaffins for further processing.

In the desorption step, a hot hydrocarbon vapor, such as butane,pentane, hexane or higher molecular weight paraffin is introduced intothe reactor. This may be supplemented by steam if desired. The aromaticsare desorbed, condensed and removed from the system. Where the paraffinused has a substantially higher vapor pressure than the lowest boilingaromatic, the aromatics can be selectively condensed and the paraffinrecycled if desired. In this desorption step, the aromatics do notdesorb entirely homogeneously; rather, the low boiling aromatics tendto. be desorbed first, followed by the intermediate boiling aromaticsand, f1- nally, by the higher boiling aromatics. By the use ofappropriate time valves, a benzene concentrate (A a toluene concentrate(A and a xylene plus higher aromatics concentrate (A can be segregated.Some isomerization of the paraffins occurs during this step.

The third step is a temperature adjustment step in which additionalhot-hydrocarbon vapor, which may or may not be the same paraffin aspreviously used, is introduced into the reactor. Normal butane'isparticularly suitable for this step. In this temperature adjustmentstep, the catalyst in the reactor causes a partial isomerization of theparaffin. In the case of normal butane particularly, the extent ofisomerization, as to isobutane, is favorable. At the temperaturescontemplated, the equilibrium ratio of normal butane to isobutane is1.5. Thus, in the temperature adjustment step, normal butane can be fedcontinuously into the reactor and a 60/40 mixture of normal andisobutane is withdrawn. Isobutane is valuable as a feed component toalkylation operations.

As a specific illustration of this invention, a system is set up toprocess 25,000 barrels per day of a certain Baton Rouge virgin naphthahaving the following composition:

Baton Rouge Virgin Naphtha Composition Continued Baton Rouge VirginNaphtha Composition Paraffins 40.5 (1) Average carbon number 8.58 (2)Average carbon number 8.58 (3) Average carbon number 8.28

Each of the three steps occurs in the reactor for a 1 minute period,thus giving a 3 minute overall cycle. Each reactor contains a mixture ofl25,000 pounds of catalyst and 60,000 pounds of adsorbent. The catalystconsists of wt.% nickel on silica-alumina having a surface area of 480square meters per gram. The adsorbent is Linde X" sieve in which 91% ofthe sodium has been exchanged for calcium.

In the reaction step, the feedstock is charged at a rate of 4,620 poundsper minute, along with 5,000 standard cubic feet (26.4 pounds) perminute of hydrogen, both at 670F. Total pressure is four atmospheresabsolute. The hydrogen partial pressure at the reactor inlet is 14.4 psi(0.98 atmospheres) and at the reactor outlet it is 46.3 psi (3.15atmospheres).

Coming out of the reactor are 2,006 pounds per minute of paraffins and22,800 standard cubic feet (121 pounds) per minute of hydrogen. Theproduct stream is cooled to 85F by heat exchange. For the first 35secends the liquid product is collected in vessel A and the separatedhydrogen released from the system. Then collection is switched to vesselB, where hydrogen is again separated and released from the system. Theliquid product collected in vessel A is predominantly isoparaftins andthat collected in vessel B is predominantly normal paraffins. In thedesorption step, butane is introduced at a rate of 3,967 pounds perminute at a temperature of 800F. The aromatics come out of the reactorat an average rate of 2,520 pounds per minute and at a temperature ofabout 630F. Since the feedstock contains hardly any six-carbonhydrocarbons,

hardly any benzene is formed. The first aromatic to appear is tolueneand this is collected in vessel E.-When xylenes begin to appear after l8seconds, the values are switched and'the remaining aromatics arecollected in vessel F. In the temperature adjustment step, butane isintroduced into the reactor at a rate of 32,767 pounds per minute, at atemperature of 700F. The 60/40 mixture of n-butane and isobutane leavesthe reactor at a temperature of 630 F.

The accompanying FIG. 2 illustrates the second aspect of the inventionin a dual reactor system. Reactors l and 2 are identical and the drawing(solid line) illustrates dehydrogenation and isomerization taken placein reactor 1 and desorption and reheating taking place in reactor 2.These reactors alternate between dehydrogenation/isomerization anddesorption/reheating. The dotted lines in the drawing show reactor 1 ibeing used for desorption and reheating and reactor 2 being used fordehydrogenation and isomerization.

The hydrocarbon feedstock comprising naphthenes and paraffins, togetherwith hydrogen, is charged via line 10 to a preheating furnace II whichraises the temperature of the feed to between about 600 and 650F. Theheated feed and hydrogen are charged via line 12 into reactor 1, whichcontains a reforming catalyst and a zeolite adsorbent as abovedescribed. In this reactor, the temperature is maintained between 600and 650F and the hydrogen pressure is maintained at between about I and4 atmospheres.

The effluent from this reactor comprising principally paraffins andhydrogen is removed via line I4. Separate streams of isoparaffinconcentrate, line 15, and nparaftin concentrate, line 16, are obtainedby means of time valve 17. If desired, a portion of the effluent streamfrom reactor 1 can be recycled via line 18 to heater 11.

Reactor 2 is, in the Figure illustrated, employed in the desorption andreheating steps. A hot hydrocarbon gas, shown as n-butane, is fed vialine 20 into reactor 2. The temperature of the gas should be betweenabout 700 to about 820F, preferably around 780F. In this reactor, thearomatics are desorbed and the isomerization catalyst contained thereinisomerizes a portion of the n-butane to isobutane. The effluent passesvia line 21 to a time valve 25 which, when properly operated, permitsthe separation of a benzene concentrate via line 22, a tolueneconcentrate via line 23, and a xylenes and higher boiling aromaticsconcentrate via line 24. Along with the various aromatic fractions,butanes will be recovered in the approximate ratio of 60% n-butane to40% isobutane.

FIG. 3 illustrates an alternate method of practicing this invention,i.e., with a fluid system. A feedstock comprising naphthenes andparaffins is charged along with hydrogen via line 30 into a furnace 31and heated to a temperature of between about 600 and 650F. It is thenfed via line 32 into reactor zone 33. In this reac tor zone, the heatedfeed is contacted with a reforming catalyst as above described and azeolite adsorbent which adsorbs the aromatic hydrocarbons as they areformed.

Reactor zone 33 is preferably a fluidized bed reactor in which thecatalyst particles are in the fluidizable size range, preferably fromabout to about 325 mesh. In this zone, the cyclopentanes are convertedto cyclohexanes and the cyclohexanes are converted to aromatics whichare adsorbed by the zeolite. Hydrogen pressure is maintained at betweenabout I and 4 atmospheres. Because of the cold conditions obtaining inreactor 33, there is virtually no hydrocracking and, furthermore,catalyst deactivation is quite slow. The paraffins in the feedstock passthrough the reactor with some isomerization, but otherwise virtuallyuneffected and are removed along with the hydrogen via line 35. Throughproper use of time valve 36, an isoparaffin stream may be removed vialine 37 by virtue of the fact that at the start of the reaction, somen-paraffins are adsorbed by the zeolite. The major portion of thenparaffins are obtained in line 38.

After the dehydrogenation and isomerization reactions in reactor 33 arecomplete, the catalyst and the zeolite are removed via control valve 39and passed via line 40 into a desorbing zone 41. n-Butane at atemperature of about 780F is introduced into the desorbing zone via line42. The aromatics adsorbed on the zeolite are removed via line 43 andpassed through time valve 44. By proper adjustment of the time valve, abenzene concentrate is first removed via line 45, followed by a tolueneconcentrate via line 46 and a xylene and higher aromatic concentrate vialine 47. Also removed at the same time is a mixture of isobutane andn-butane in a ratio of about 60 to 40.

After the desorption is complete, the catalyst and zeolite are removedvia line 48. The catalyst is then regenerated in the ordinary manner bymeans not shown and returned to reactor 33. As will be recognized bythose skilled in the art, continuous movement of the solids from onevessel to the other and back again, with or without intermediateregeneration in a third vessel with air can also be practiced.

The invention thus provides a means of catalytically reformingnaphthenes to the virtual exclusion of undesirable side reactions suchas cracking. Some isomerization of paraffms also occur. In addition, ifthe second aspect of this invention is used, i.e., the adsorption ofaromatics formed in the course of the reaction, some separation ofisoparaffins from n-paraffins and also the partial isomerization of theparaffin hydrocarbon vapor (e.g. n-butane) used in the desorption ofzeolite on which the aromatics have been adsorbed can be achieved. Amotor fuel of improved octane number is thus obtained through aneconomically attractive process.

Other modifications of the present invention will occur to those skilledin the art upon a reading of the present disclosure. These are intendedto be included within the scope of this invention.

What is claimed is:

1. A process for reforming a hydrocarbon feedstock comprising naphthenesand paraffms in which the naphthenes are converted to aromatichydrocarbons, which process comprises contacting said feedstock in areforming zone with a dehydrogenation and isomerization catalyst at atemperature of between about 600 and 700F., maintaining a hydrogenpressure of4 atmospheres or less, and providing in the reforming zone asolid adsorbent mixed with the catalyst for adsorbing the aromatichydrocarbons as they are produced.

2. A process according to claim 1 in which the hydrogen partial pressureranges from about 1 atmosphere to about 4 atmospheres.

3. A process according to claim 2 in which the solid adsorbent is analuminosilicate molecular sieve which selectively adsorbs aromatichydrocarbons to the substantial exclusion of naphthenes.

4. A process according to claim 3 in which the aluminosilicate molecularsieve has a pore diameter of about 13 A.

5. A process according to'claim 3 in which the aluminosilicate molecularsieve having aromatic hydrocarbons adsorbed thereon is subjected to adesorbing step.

6. A process according to claim 5 in which the desorbing is accomplishedby contacting the aluminosilicate molecular sieve with hot hydrocarbonvapor.

7. A process according to claim 6 in which the hydrocarbon is n-butane.

8. A process according to claim 6 in which the hydrocarbon is a mixtureof n-butane and isobutane.

9. A process according to claim 6 in which the desorption step isperformed at a temperature of between about 700 and 800F.

10. A process according to claim 6 which comprises, after the desorptionstep, the additional step of adjusting the temperature of the catalystand aluminosilicate molecular sieve adsorbent to a temperature ofbetween 600 and 700F.

11. A process according to claim 3 in which the hydrocarbon feedstock isa hydrocrackate comprising principally cyclopentanes and cyclohexanes.

12. A process according to claim 3 in which the catalyst comprisesnickel on an acidic support.

13. A process according to claim 12 in which the catalyst comprises fromabout 1.0 to about 10% of nickel on a silica-alumina catalyst.

14. A process according to claim 13 in which the catalyst is anickel-silica-alumina catalyst having about 5% nickel.

15. A process according to claim 3 in which the catalyst comprises fromabout 0.025 to 1.0 wt. of a noble metal on an acidic or non-acidicsupport.

16. A process according to claim 15 in which the catalyst comprises fromabout 0.1 to about 1.0% of a noble metal on a non-acidic support.

17. A process according to claim 16 in which the sup port is aluminapromoted by chlorine or fluorine.

18. A process according to claim 16 in which the noble metal isplatinum.

19. A process according to claim 17 in which the catalyst is aplatinum-chlorine-alumina catalyst.

20. A process for reforming a hydrocrackate comprising principallycyclopentanes and cyclohexanes in which the cyclopentanes andcyclohexanes are converted to aromatic hydrocarbons, which processcomprises contacting said hydrocrackate in a reforming zone, at atemperature between 600 and 700F., with a dehydrogenation andisomerization catalyst comprising from about 0.1 to about 1.0% platinumon a chlorided alumina support, maintaining a hydrogen partial pressureof 4 atmospheres or less, and providing in .the- I reforming zone analuminosilicate molecular sieve adsorbent having a pore diameter ofabout 13 A, which selectively adsorbs the aromatic hydrocarbons as theyare formed.

21. A process according to claim 20 in which the aluminosilicatemolecular sieve having aromatic hydrocarbons adsorbed thereon issubjected to a desorbing step which comprises contacting saidaluminosilicate molecular sieve with n-butane at a temperature ofbetween about 700 and 800F.

1. A PROCESS FOR REFORMING A HYDROCARBON FEEDSTOCK COMPRISING NAPHTHENESAND PARAFFINS IN WHICH THE NAPHTHENES ARE CONVERTED TO AROMATICHYDROCARBONS, WHICH PROCESS COMPRISES CONTACTING SAID FEEDSTOCK IN AREFORMING ZONE WITH A DEHYDROGENATION AND ISOMERIZATION CATALYST AT ATEMPERATURE OF BETWEEN ABOUT 600* AND 700*F., MAINTAINING A HYDROGENPRESSURE OF 4 ATMOSPHERES OR LESS, AND PROVIDING IN THE REFORMING ZONE ASOLID ADSORBENT MIXED WITH THE CATALYST FOR ADSORBING THE AROMATICHYDROCARBONS AS THEY ARE PRODUCED.
 2. A process according to claim 1 inwhich the hydrogen partial pressure ranges from about 1 atmosphere toabout 4 atmospheres.
 3. A process according to claim 2 in which thesolid adsorbent is an aluminosilicate molecular sieve which selectivelyadsorbs aromatic hydrocarbons to the substantial exclusion ofnaphthenes.
 4. A process according to claim 3 in which thealuminosilicate molecular sieve has a pore diameter of about 13 A.
 5. Aprocess according to claim 3 in which the aluminosilicate molecularsieve having aromatic hydrocarbons adsorbed thereon is subjected to adesorbing step.
 6. A process according to claim 5 in which the desorbingis accomplished by contacting the aluminosilicate molecular sieve withhot hydrocarbon vapor.
 7. A procesS according to claim 6 in which thehydrocarbon is n-butane.
 8. A process according to claim 6 in which thehydrocarbon is a mixture of n-butane and isobutane.
 9. A processaccording to claim 6 in which the desorption step is performed at atemperature of between about 700* and 800*F.
 10. A process according toclaim 6 which comprises, after the desorption step, the additional stepof adjusting the temperature of the catalyst and aluminosilicatemolecular sieve adsorbent to a temperature of between 600* and 700*F.11. A process according to claim 3 in which the hydrocarbon feedstock isa hydrocrackate comprising principally cyclopentanes and cyclohexanes.12. A process according to claim 3 in which the catalyst comprisesnickel on an acidic support.
 13. A process according to claim 12 inwhich the catalyst comprises from about 1.0 to about 10% of nickel on asilica-alumina catalyst.
 14. A process according to claim 13 in whichthe catalyst is a nickel-silica-alumina catalyst having about 5% nickel.15. A process according to claim 3 in which the catalyst comprises fromabout 0.025 to 1.0 wt. % of a noble metal on an acidic or non-acidicsupport.
 16. A process according to claim 15 in which the catalystcomprises from about 0.1 to about 1.0% of a noble metal on a non-acidicsupport.
 17. A process according to claim 16 in which the support isalumina promoted by chlorine or fluorine.
 18. A process according toclaim 16 in which the noble metal is platinum.
 19. A process accordingto claim 17 in which the catalyst is a platinum-chlorine-aluminacatalyst.
 20. A process for reforming a hydrocrackate comprisingprincipally cyclopentanes and cyclohexanes in which the cyclopentanesand cyclohexanes are converted to aromatic hydrocarbons, which processcomprises contacting said hydrocrackate in a reforming zone, at atemperature between 600* and 700*F., with a dehydrogenation andisomerization catalyst comprising from about 0.1 to about 1.0% platinumon a chlorided alumina support, maintaining a hydrogen partial pressureof 4 atmospheres or less, and providing in the reforming zone analuminosilicate molecular sieve adsorbent having a pore diameter ofabout 13 A, which selectively adsorbs the aromatic hydrocarbons as theyare formed.
 21. A process according to claim 20 in which thealuminosilicate molecular sieve having aromatic hydrocarbons adsorbedthereon is subjected to a desorbing step which comprises contacting saidaluminosilicate molecular sieve with n-butane at a temperature ofbetween about 700* and 800*F.